Do lysins drive resistance like antibiotics?

Why antibiotics breed resistance

An antibiotic has to get inside the bacterium and switch off a specific protein or process. That opens six well-mapped escape routes: bacteria can pump the drug back out, lock the doors it enters through, produce enzymes that destroy it, mutate the target so the drug no longer fits, build a drug-proof substitute, or simply swap the resistance gene with a neighbour.

Each of these changes something the cell can afford to lose. And because antibiotics kill slowly, over many bacterial generations, a single rare resistant cell has time to multiply while the drug clears the rest. Resistance to a new antibiotic is usually detectable within a year or two of widespread use.

Why lysins are different

Lysins are enzymes that bacteriophages evolved to cut open the bacterial cell wall, a mesh called peptidoglycan. That wall is the bacterium’s skeleton: a single, continuous, woven molecule holding the cell together against enormous internal pressure. A lysin snips one of its load-bearing bonds and the cell bursts in seconds, like a balloon.

Crucially, a lysin works from outside the cell and never goes in. So the six antibiotic escape routes, which all operate inside the cell or at its membrane, are pointed the wrong way. There is nothing to pump out, no door to lock, no internal target to mutate. The only theoretical escape is to rebuild the wall itself, and a bacterium cannot do that without dying.

What the evidence shows

This is not only theory. In a 28-day head-to-head laboratory study, the gold standard for measuring how fast resistance emerges, a lysin and three antibiotics were pushed under identical conditions. The antibiotics became 8, 16 and 32 times harder to use. The lysin needed exactly the same dose on day 28 as on day 1: zero drift.

The same pattern holds across many lysins and 40+ passage cycles, in a decade of real-world surveillance, and across six lysins tested in human clinical trials, where not a single case of lysin resistance has ever been recorded. Remarkably, adding a trace of lysin alongside an antibiotic can even suppress the resistance the antibiotic would otherwise develop.

The honest position

We are careful not to overclaim, because candour is more persuasive than absolutes. There is a non-zero chance of lysin resistance. What the structural biology and the data show is that it is orders of magnitude less probable than antibiotic resistance, not that it is impossible.

Even the one peptidoglycan-targeting enzyme where resistance has been forced in the lab, lysostaphin, produces mutants that grow 4–5× slower, are at least 5× less virulent, and revert to being treatable by ordinary antibiotics. Even the worst case is a self-limiting dead end.

Why this matters even more for personal care

ArrowBiome’s lysins are INCI cosmetic actives applied to skin, not systemic drugs. Every factor that drives resistance in a hospital is weaker or absent in a rinse-off, species-selective topical: no lingering low dose, no exposure to the gut’s reservoir of resistance genes, and no flattening of the beneficial skin community. The use-case lowers an already low risk.